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iXon 3

Features & Functionality

3.4.2.1 - Points to note about using an FT CCD as a standard CCD

• Theexposuretime,accumulationcycletimeandthekineticcycletimeareindependent.

• Theminimumexposuretimeisnotrelatedtothetimetakentoreadouttheimage.

• ExternaltriggeroperatesasiftheCCDwasanNFTCCD.

• AsthecapturedimageisquicklyshiftedintotheStoragearea,eveninNFTmode,thesystemcanstillbeused

without a mechanical shutter.

• ForshortexposuretimestheimagemayappearstreakedasthetimetakentoshifttheImageareaintothe

Storage area and the exposure time may be of similar magnitude, but much less than a ral non-frame transfer.

• LightfallingontheImageareawhiletheStorageareaisbeingreadoutmaycontaminatetheimageinthe

Storage area due to charge spilling vertically along a column from the Image area. The slower the read-out rate

or the shorter the exposure time the greater the possibility of corruption. To see why this is the case consider

the following situation:

“During a 100us exposure enough light has fallen on a pixel to register 10000 counts, or 100,000 electrons

assuming 10e/count. The image is then shifted into the Storage area. To read out the image, assuming

1000x1000 pixels, it would take approximately 100ms at 10MHz readout rate. This means that during the reading

out of the image 10 million counts (10000 * 1000) will have been acquired into the pixel described above. As a

pixel saturates at approximately 160,000 electrons this means that the pixel will over saturated by 60 times. All

the excess charge has to go somewhere, and spreads vertically along the CCD column. As the clocks in the

Image area are not actively shifting the charge, the mobility of the charge will be low and you may not see any

effect. However, when you consider that more than one pixel in any given column could be exposed to 10000

counts per 100μs. The chance of corrupting data is correspondingly increased. Reducing the amount of light

falling on the CCD outside of the exposure period and increasing the exposure time accordingly will reduce the

possibility of data corruption”.

Andor Technology iXon3 Series User Manual

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